Cracked tank on Toto Drake

I had a new Toto Drake installed less than a month ago by a licensed plumber and today I noticed that the tank has cracked around the handle and the crack is moving down the tank. I know the cracks were not there immediately after install. I am wondering if this was caused by the handle being installed incorrectly or if it is a defect in the toilet tank. Has anyone had this problem? I am just wondering if I should be calling the plumber or Toto tomorrow.

I'd start with the plumber. Let him deal with handling the replacement from Toto. My guess is there was a flaw that was evident when the toilet was inspected at the factory or when the plumber installed it. Other than the inconvenience, I doubt if there will be a problem with the replacement.

Unfortunately I did not purchase the toilet directly from the plumber, I purchased it from the plumbing supply and he just installed it. I am thinking that the handle was tightened too much or something like that from the way the cracks have appeared. I did inspect the toilet carefully before it was installed and there were no cracks in the tank at that time, and there were also no cracks in the first 2 weeks of using the toilet (I know this because I would have noticed them when I was cleaning). The cracks are very noticable now so I am sure they just started forming in the last few days. I am also thinking I should be calling the plumber but I just wondered if anyone had experienced a problem like this also in case they try to blame the cracks on a defective tank and tell me to call Toto.

Toto makes a good product, but some defects do get past them. I installed three drakes at my home a couple of years ago and one of them had a deformed tank. It wasn't an obvious deformity even when installed. It was slightly askew so that the cover didn't fit evenly/flush and it had a slight twist that made it look like the tank wasn't on straight no matter how I adjusted it. Some measurements of both sides confirmed what my eyes were seeing. So I swapped it out at the supply house, showing them what the problem was.

Perhaps the plumber can run the interference for you arranging for you to swap the tank at the supply house? He probably does enough business with them that if he tells them the tank was/is faulty they will take it back. Or if he made a mistake in the install that has resulted in a crack, perhaps he will see and admit it.

I would be wary of growing cracks, wouldn't want the tank to start leaking water all over.

A trip lever won't cause a crack. It's a plastic nut. It would strip out before it could be tightened that much. Normally when I see a crack from the hole for the trip lever, I think something like; the tank was dropped on the handle at some point.
Of the thousands we sell, it's extremely rare. I did see that very thing on a tank that was installed by a plumber on one of the islands here in Washington.

If the crack wasn't there when it was installed then something must have happened to crack it. Most toilets come with the handle already installed out of the box so if this was the cause (unlikley), it would be the manufactures fault not the plumbers.

I've seen people not notice cracks before. I tap the tanks to see if they "ring" or not. After things get some dirt on them, they become more visible.
I've seen people drop tanks on the concrete, holding the box with one hand, the cardboard tears away and whap! Down it goes.

If you bought the toilet, it has nothing to do with the plumber, because he did not "install" the handle, assuming that is what caused the crack. It is up to you to remove the tank, exchange it, and reinstall it, unless you wish to pay the plumber to do it for you.